A Frequency Modulation (FM) receiver receives FM signals from an FM broadcasting station. Currently, to automatically scan a valid transmission, the FM receiver finds FM broadcasting stations with valid transmissions or frequency locks to a next FM broadcasting station having a valid transmission. Due to interference from other radio circuits, or due to non-linear analog front end of the FM receiver, a condition called false frequency lock can occur in the FM receiver. The false frequency lock can lead to a noisy output as the FM receiver locks to a frequency signal other than a desired signal or a valid signal. Therefore, there is a need for an FM receiver that avoids false frequency locks during autonomous scan.
In an existing technique to avoid false frequency locks, two metrics are used to determine if a frequency signal corresponds to the valid signal. First metric is Received Signal Strength Indication (RSSI). The RSSI indicates energy of an FM signal. If the RSSI is greater than a threshold, then an FM channel is found to have a valid transmission. The threshold is based on sensitivity. Second metric is Intermediate Frequency (IF) count. The IF count indicates nominal centre frequency of the FM signal. Ideally, the IF count has a value of zero. If the IF count is lesser than an expected mismatch between an FM transmitter and the FM receiver, the FM channel is found to have a valid transmission. However, when interferences from other radio circuits fall in a frequency channel of interest, the metrics fail to prevent false frequency lock. Also, the false frequency lock can occur when harmonics of signals at other frequencies fall in a frequency channel of interest. Further, the false frequency lock may also occur when two signals of similar strength from two valid stations are centered at either end of the frequency channel of interest.